Modular multilevel converters (MMC) are inverters where high voltages are generated in that some or even several hundred modules are connected in series such that the series connection is each connected to the positive or negative DC voltage and a phase, e.g., the first phase of the three-phase current, respectively. Each module has, for example, its individual IGBT phase and can be switched independent of the other modules. Thus, it becomes possible that the generated AC voltage can be switched in as many level steps as submodules exist. With several hundred submodules, an almost perfect sinusoidal shape can be generated.
Normally, in the arm consisting of the individual submodules, a so-called arm inductance is provided that serves to smooth the output voltage and hence to increase the output voltage quality (AC side). For obtaining improved output voltage quality, for example, the arm inductance is increased. The arm inductance also limits the current rise velocity which can reduce the switching frequency and the regulator velocity.